depends on what is important to you, if you're purely talking sound quality it is generally considered the SGP 4.0 has the better DAC, the 4.0 also has an easy to replace battery (important selling point to some people) and a proximity sensor, where the 5.0 lacks the proximity sensor but has a flash for the camera, then of course there is the screen size difference, the Cowon players are universally known for sound quality but they are smaller screens, I can't speak to other aspects of them as I haven't had any myself. I used to have an Archos 5 (pre android version) it totally lacked a camera but had a great screen (atleast compared to other devices of the time) and since it still used the micro 1.8" hard drives you could get 60GB of storage on the internal with 2 other models have 120GB and 250GB capacities, the android versions of the archos 5 switched to flash memory and so they dropped to the standard 32GB of storage but added an SD card slot.

I find all andriod PMP's tend to excel in certain areas and lack in others so it's fairly hard to say something is "on par" with another one because it really depends on what features are most important to you.